A spark plug is a component that generates spark discharge in order to ignite an air-fuel mixture in a combustion chamber. As a structure of the spark plug, there is known a structure that includes: a ceramic insulator in which an axial hole is provided so as to extend along an axis; a metal shell that holds the ceramic insulator therein; a center electrode held in the axial hole; and a conductive seal body for holding the center electrode in the axial hole (Patent Document 1). In the case of the structure disclosed in Patent Document 1, the center electrode includes a flange portion projecting in a radial direction, and a head portion protruding from the flange portion toward a rear end side, and by using this structure, the center electrode is held in the ceramic insulator. Specifically, by the flange portion abutting against a stepped portion provided in the axial hole, the center electrode is prevented from moving toward a front end side. In addition, by the seal body being filled into a portion around the head portion and the flange portion, impact resistance of the center electrode is secured, whereby loosening of the center electrode is less likely to occur even when the center electrode is subjected to impact by combustion.